This invention relates to a process for treating aluminum batchwise or continuously to form an unsealed, porous anodic oxide layer thereon with discrete metal islands electrolytically deposited in the pores of the oxide layer and extending above the surface thereof in a bulbous, undercut configuration. This invention also relates to an article having an aluminum substrate, an unsealed, porous anodic oxide layer and randomly distributed discrete metal islands anchored in the pores of the oxide layer.
The art of surface treating and finishing of aluminum and its alloys is a complex and well developed art as evidenced by the texts of S. Wernick entitled Surface Treatment and Finishing of Aluminium and Its Alloys, Robert Draper Ltd., Teddington, England (1956) and G. H. Kissin Finishing of Aluminum, Reinhold Publishing Corporation, New York. It is acknowledged that electroplating on aluminum requires extraordinary treatments to gain the necessary adhesion. The most familiar techniques for plating on aluminum are the zincating and anodizing processes. In the latter case which involves the plating over an anodic oxide layer formed on an aluminum substrate, the art has directed its efforts towards producing continuous electroplated coatings.
It has now been discovered that a discontinuous electroplated metal surface can be applied to anodized aluminum in an efficient and economical manner. This discontinuous electroplated surface provides articles useful per se, for example as composite catalyst bodies, and because the discontinuous electroplated surfaces tenaciously adheres and interlocks with the anodic oxide layer on the aluminum, it is now possible to directly apply coatings and laminates to the aluminum article thereby forming a tenacious, mechanically interlocked bond to the coating.